Your synastry score, calculated from both births. Free and instant.
This score doesn't compare two Sun signs: it overlays your two complete birth charts. Two people with the same sign can have radically different synastries, it all depends on the time, the place, and what the rest of the sky is doing.
The tool casts both exact charts on the JPL (NASA) precision ephemerides, from both dates, times and places of birth. It then measures the inter-chart aspects: the angles that one person's planets form with the other's. Each aspect is weighted by the planets involved and the tightness of the orb, a close Venus-Moon conjunction doesn't weigh like a wide Mars-Saturn square. The weighted sum gives your percentage, computed by the same engine as our full Synastry.
The score says how much your two skies agree, not where or why: the precise aspects, the areas at play (love, communication, values) and the detailed reading are what the full Synastry is for.